1. Field of the Invention
The present invention related to a compression ignition internal combustion engine of a premixed mixture type, and in particular to a method of controlling ignition timing of a compression ignition engine of a premixed mixture type, which can optimumly control the timing of compression ignition.
2. Related Art
These years, there has been proposed a compression ignition internal combustion engine of a premixed mixture, which utilizes a combustion system for compressing homogenous premixed gas so as to cause self-ignition of the premixed gas. This engine can carry out its operation in an ultra lean mixture range (in which the air-fuel ratio is higher than 80%), which cannot be carried by a conventional gasoline or Diesel engine, and accordingly, the flame temperature can be lowered and the homogenous mixture gas can carry out ignition and combustion by itself. Thus, this engine can greatly reduce emission of both NOx and soot.
In general, when premixed gas is compressed so as to raise its temperature to a given value, the so-called low temperature oxidation reaction is initiated by dehydrogenation of hydrocarbon as a fuel. After the low temperature oxidation reaction is progressed, self-ignition of the premixed gas occurs by way of the so-called blue flame elementary reaction. Since this self-ignition phenomenon simultaneously occurs at multiple points in the mixture gas, the period of combustion as viewed in the entire combustion chamber is extremely shorter than that by spark ignition (simple point ignition) in a conventional gasoline engine or that of spray combustion in a Diesel engine. This fact results in restraint of production of NOx which depends upon the temperature of flame and the duration thereof, and accordingly, it mainly realizes reduction of NOx in the compression ignition internal combustion engine.
The combustion period in a conventional spark ignition engine which depends upon flame propagation caused after spark ignition by a spark plug tends to become shorter as the engine speed becomes higher. This is because the intensity of turbulence in an air stream created within the combustion chamber becomes higher as the engine speed increases, and as a result, the area of the surface of the flame (the reaction area) increases. Accordingly, in the spark ignition engine, the heat generation crank angle which can exhibit a time of heat generation can be maintained to be substantially constant, irrespective of its engine speed.
On the contrary, in a compression ignition engine of a premixed mixture type, it has been known that the self-ignition phenomenon is caused simultaneously at multiple points in the mixture gas, and accordingly, the combustion period is extremely shorter than that of the spark ignition engine, and is substantially constant, irrespective of an engine speed. This is because the fuel is burnt through compression ignition so that the combustion occur simultaneously over the entire area of the combustion chamber through the compression of ignition of premixed mixture gas, and accordingly, no flame surface is present so that it cannot hardly be affected by a gas stream. Accordingly, in the compression ignition engine of a premixed mixture type, the heat generation crank angle varies, depending upon an engine speed, that is, the lower the engine speed, the longer the combustion crank angle, and vise versa.
A reciprocating engine which carries out Otto cycle which is representative of gasoline engines, exhibits a highest degree of thermal efficiency around the top dead center of compression at which the heat generation becomes maximum. In the case of the compression ignition engine of a premixed mixture type, since the self-ignition phenomenon is effected at multiple points in mixture gas so that the period of combustion is substantially constant, irrespective of an engine speed, the crank angle at which the heat generation is maximum varies, depending upon an engine speed, and accordingly, the crank angle at which the heat generation is maximum becomes out of a zone around the top dead center, depending upon an engine speed. Accordingly, in the compression ignition engine of a premixed mixture type, it is required to precisely control the ignition timing so as to obtain a maximum value of heat generation around the top dead center of compression at every engine speed in order to maximize the thermal efficiency.
However, in the case of the compression ignition engine of a premixed mixture type, since there is used the self ignition through which mixture gas in the combustion chamber is self-ignited by compression heat that is produced when the mixture gas is compressed by a piston, without using a spark plug, in a range of compression ignition of premixed mixture gas, the control of the ignition timing with a high degree of accuracy is difficult in comparison with control of spark ignition through which the supply of power to a spark plug is controlled as in the case of a spark ignition engine.
In order to solve the above-mentioned problems, JP-A-2000-220482, as prior art, proposes a method of controlling the timing of compression ignition by liquid which can absorb latent heat from premixed gas after the mixing volume of the liquid is adjusted since the timing of compression ignition can be controlled by the liquid which is mixed in the premixed gas so as to absorb latent heat from the latter upon evaporation thereof.
Further, JP-A-2000-265867 proposes a method in which there is provided such a configuration that the timing of compression ignition can be detected during operation cycle of an engine, and control gas which has a specific heat ratio different from that of the premixed gas and which does not react in the combustion chamber can be fed into the combustion chamber, and accordingly, the supply volume of the control gas to be fed into the combustion chamber is controlled in accordance with a detected ignition timing.
Further, JP-A-2000-227027 proposes a method of controlling the timing of compression ignition in which the timing of compression ignition can be detected during operation cycle of an engine while a means for controlling the temperature of intake air is provided in a part upstream of an intake port, and accordingly, the timing of ignition is controlled by controlling the temperature of intake air fed into the combustion chamber in accordance with a detected timing of ignition.
Further, JP-A-10-238374 proposes a method in which there are provided an ignition fuel injector which starts ignition within a combustion chamber in association with an ignition timing in the combustion chamber, a compression ratio changing mechanism for changing the volume of the combustion chamber so as to change the compression ratio and a control means for adjusting the volume of premixed mixture fuel and the compression ratio in accordance with a load condition of the internal combustion engine, and accordingly, the compression ratio is changed in accordance with a volume of premixed mixture which depends upon a load condition while ignition fuel is fed in association with an ignition timing so as to start the combustion.
However, the above-mentioned prior art examples have raised problems as stated below:
In the method disclosed in the JP-A-2000-220482, since the timing of compression ignition is controlled by mixing the liquid for absorbing latent heat of evaporation, into the mixture gas, a pump for charging the liquid, a tank for reserving the liquid, and a control valve for controlling the charge volume of the liquid are required in addition to a conventional engine, and accordingly, there are presented problems of increased costs, requirement of a space for attachment of the above-mentioned equipment, and complication in the periodical replenishment of the liquid.
Further, in a method disclosed in the JP-A-2000-265867, since the timing of compression ignition is controlled by mixing control gas into mixture gas, a pump for charging the control gas, a tank for reserving the gas and a control valve for controlling the volume of the control gas are required in addiction to a conventional engine, and accordingly, there are presented problems of increased costs, requirement of a space for attachment of the above-mentioned equipment, and complication in the periodical replenishment of the control gas.
Further, in the method disclosed in the JP-A-2000-227027, since the temperature of intake air fed into a combustion chamber is controlled so as to control the timing of compression ignition, a means for controlling the temperature of the intake air is required in addition to a conventional engine, there are presented problems of increased costs, and requirement of a space for attachment of the above-mentioned equipment. Further, since a means for heating or cooling the intake air is provided to the intake port, there is presented such a problem that the control of the timing of self-ignition with a high degree of accuracy becomes difficult due to a response lag in the temperature of the intake air.
Further, in the method disclosed in the JP-A-10-238374, since the compression ratio is changed in accordance with a volume of premixed fuel which depends upon a load condition while ignition fuel is fed in association with an ignition timing, the configuration for changing the compression ratio of the combustion chamber becomes complicated, and accordingly, there are presented problems of lowering of reliability and increased costs.
An object of the present invention is to provide a method of controlling the timing of ignition of a compression ignition engine of a premixed mixture type, which can optimumly control the timing of compression ignition in association with an operating condition of the engine at a low cost without complicating the configuration thereof.
The essential feature of the present invention is the provision of a compression ignition engine of a premixed mixture type in which premixed gas is self-ignited through compression by a piston, with a method in which the volume of sprayed fuel impinging upon the inner wall surface of a combustion chamber is continuously or stepwise increased as the engine speed varies from a low speed to a high speed in a compression ignition operating range.
Another essential feature of the present invention is to provide a compression ignition engine of a premixed mixture type in which premixed gas is self-ignited through compression by a piston, with a method in which a fuel injector for injecting fuel into an intake port for feeding air into a combustion chamber is provided, and the fuel injection timing of sprayed fuel adapted to be injected into the intake port from the fuel injector is continuously or stepwise advanced from intake stroke injection to compression stroke injection as the engine speed varies from a low speed to a high speed in a compression ignition operating range.
Further another essential feature of the present invention is to provide a compression ignition engine of a premixed mixture type in which premixed gas is self-ignited through compression by a piston, with a method in which there are provided a pressure sensor for detecting a pressure in a combustion chamber and a crank angle sensor for detecting a rotating angle of a crank shaft, the timing of ignition is controlled so that a maximum value of pressure in the combustion chamber, which is detected by the pressure sensor, is obtained in a crank angle range from 10 to 15 deg. after the top dead center of compression, in a compression ignition operating range.
The present invention will be detailed in the form of preferred embodiments with reference to the accompanying drawings in which: